Preparation of paper having improved wet strength



United States Patent 9 PREPARATION OF PAPER HAVING IMPROVED WET STRENGTH Carl W. Schroeder, Orinda, Calif., assignor to Shell l )e velopment Company, New York, N.Y., a corporation of Delaware N Drawing. Application June 28, 1955 Serial No. 518,667

14 Claims. (Cl. 117-155) This invention relates to paper, and more particularly, to a process for preparing paper having improved wet strength and other superior properties.

Specifically, the invention provides a new and efiicient process for preparing paper having unexpectedly high wet tensile strength which is of a permanent nature, excellent fold endurance, good absorbency and improved resistance to acids and alkali. This process comprises applying to the paper pulp or paper, at some time during the production of the paper up to and including the finished paper, by means of an aqueous medium (1) a polyether polyepoxide and (2) an epoxy curing agent, and then drying the product and curing the polyepoxide within the paper fibers. The invention further provides wet strength paper produced by this method.

Ordinary paper when wet loses its strength and is easily torn. In order to overcome this shortcoming, it

'has been common practice to treat the paper with a nitrogen-containing resin, such as ureaor melamineformaldehyde resin, that can be subsequently cured to form an insoluble resin. While this method has imparted some improvement in wet strength, it still fails to give a product having properties required for many commercial applications. The wet tensile strength provided by this method, for example, is sometimes not as high as desired. In addition, the improvement in wet strength is only temporary and is readily lost aftershort periods of exposure to water. This has been found to be due in part to the fact that the cured nitrogencontaining resin is easily hydrolyzed, particularly in the presence of the acid curing agents remaining in the resin. This defect as to poor resistance to hydrolysis is particularly serious as it prevents continued use of the paper as well as use for applications, such as food wrappers or containers where there is danger of having some toxic action on the material enclosed. In addition, the paper treated in this manner generally loses its customary feel, becomes quite brittle, loses some of its absorbency and has poor fold endurance. Furthermore, paper treated as above usually has rather poor resistance to acids and/or alkali and are unsuited for use where the paper must come in contact with these chemicals.

It is an object of the invention, therefore, to provide a new process for the production of paper. It is a further object to provide a new process for preparing paper having unexpectedly high wet tensile strength and burst strength. It is a further object to provide a new process for preparing wet strength paper having high wet strength which is of a permanent nature and is not lost through hydrolysis. It is a further object to provide wet strength paper which is relatively non-toxic and useful in preparing food wrappers and containers. It is still a further object to provide a method for preparing wet strength paper which has normal feel, excellent fold endurance and good absorbency. It is further object 2,913,356 Patented Nov. 17,- 1959 2 to provide a method for preparing paper having good resistance to acids and alkali. It is still a further object to provide wet strength paper and paper products having improved properties. Other objects and advantages of the invention. will be apparent from the following de* tailed description thereof.

It has now been discovered that these and other objects may be accomplished by the process of the invention which comprises applying to the paper pulp or paper, at some time during the production of the paper up to and including the finished paper, by means of an aqueous medium (1) a polyether polyepoxide and (2) an epoxy curing agent, and then drying the product and curing the polyepoxide within the paper fibers. It has been found that paper prepared in this manner has unexpectedly high wet tensile strength and burst strength. Furthermore, this improvement in strength is permanent and is not lost through hydrolysis as is the case with the wet strength obtained by use of the conventional resins. The treated paper is also non-toxic and useful for preparation of food wrappers and containers. Further the improvement as to wet strength is obtained without change in feel, appearance or absorbency of the paper, and the treated paper has surprisingly good resilience and good fold endurance. This makes the paper suitable for use for all types of wrappings and containers, for :paper towels and tissues, paper drapes, cord, maps and the like. In addition, the above process yields paper having good resistance to both acids and alkali and thus suited for use in preparing paper for construction purposes, battery manufacture and the like.

The polyether polyepoxides to be used in the process of the invention comprise those compounds possessing at least two ether linkages (i.e., --O- linkages) and a plurality of 1,2-epoxy groups These polyether polyepoxides may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic and may be substituted if desired with various substituents, such as halogen atoms, hydroxyl groups, ether radicals, and the like. They may also be monomeric or polymeric.

For clarity, many of the polyether polyepoxides and particularly those of the polymeric type will be described throughout the specification and claims in terms of an epoxy equivalency. The term epoxy equivalency as used herein refers to the average number of epoxy groups contained in the average molecule. This value is obtained by dividing the average molecular weight of the polyepoxide by the epoxide equivalent Wight. The epoxide equivalent weight is determined by heating'a onegram sample of the polyepoxide with an excess of pyridinium chloride dissolved in pyridine. The excess pyridinium chloride is then back titrated with 0.1 N sodium hydroxide to phenolphthalein end point. The epoxide value is calculated by considering one HCl as equiv alent to one epoxide group. This method is used. to obtain all epoxide values reported herein.

If the polyether polyepoxide material consists of a single compound and all of the epoxy groups are intact, the epoxyequivalency will be integers, such as 2,. 3, 4, and the. like. However, in the case of polymeric-type polyether polyepoxides many of the materials may con tain some of the monomeric monoepoxidesor have'some of their epoxy groups hydrated or otherwise reacted and/or contain macromolecules of somewhat difierent molecular weight sothe epoxy equivalency may be quite low and contain fractional values. The polymeric material may, for example, have an epoxy equivalency of 1.5, 1.8, 2.5, and the like.

Polyether polyepoxides to be used in the process of the invention may be exemplified by 1,4-bis(2,3-epoxypropoxy)benzene, l,3-bis-(2,3-epoxypropoxy)benzene, 4,4- bis(2,3-epoxypropoxy)diphenyl ether, 1,3-bis(2,3-epcxypropoxy)octane, 1,4-bis(2,3-epoxypropoxy)-cyclohexane, 4,4'-'bis (Z-hydroxy 3,4 epoxybutoxy) diphenyldimethylmethane, 1,3-bis-(4,5-epoxypentoxy)-5-chlorobenzene, l, 4-bis(3,4-epoxybutoxy)-2-ch1orocyclohexane, diglycidyl ether, ethylene glycol diglycidyl ether, resorcinol diglycidyl ether, and 1,2,3,4-tetra(2-hydroxy-3,4-epoxybutoxy)- butane.

r Other examples include the glycidyl polyethersof polyhydric phenols obtained by reacting a polyhydric phenol with an excess, e.g., 4 to, 8 mole excess, of a chlorohydrin, such as epichlorohydrin and dichlorohydrin. Thus, Polyether D described hereinafter, which is substantially 2,2-bis(2,3-epoxypropoxyphenyl)propane, is obtained by reacting bis-phenol-A(2,2-bis(4'-hydroxyphenyl)propane) with excess of epichlorohydrin in an alkaline medium. Other polyhydric phenols that can be used for this purpose include resorcinol, catechol, hydroquinone, methyl resorcinol, or polynuclear phenols, such as 2,2-bis-(4-hydroxyphenyl)butane, 4,4'-dihydroxyben zophenone, bis(4-hydroxyphenyl)ethane, and 1,5-dihydronaphthaleneJ Still a further group of the polyether polyepoxides comprises the polyepoxy polyethers obtained by reacting, preferably in the presence of an acid-acting compound, such as hydrofluoric acid, one of the aforedescribed halogencontaining epoxides with a polyhydric alcohol, and subsequently treating the resulting product with an alkaline component. As used herein and in the claims, the expression polyhydric alcohol is meant to include those compounds having at least two free alcoholic OH groups and includes the polyhydric alcohols and their ethers and esters, hydroxy-aldehydes, hydroxy ketones, halogenated polyhydric alcohols, and the like. Polyhydric alcohols that may be used for this purpose may be exemplified by glycerol, propylene glycol, ethylene glycol, diethylene glycol, butylene glycol, hexanetriol, sorbitol, mannitol, pentaerythritol, polyallyl alcohol, polyvinyl alcohol, sorbitol, mannitol, inositol, trimethylolpropane, bis(4-hydroxycyclohexyl)dimethyl-methane, 1,4-dimethylolbenzene, 4,4'-dimethyloldiphenyl, dimethylol toluenes, and the like. The polyhydric ether alcohols include, among others, diglycerol, triglycerol, dipentaerythritol, tripentaerythritol, dimethylolanisoles, beta hydroxyethyl ethers of polyhydric alcohols, such as diethylene glycol, polyethylene glycols, bis(beta hydroxyethyl ether) of hydroquinone, bis(beta hydroxyethyl ether) of bis-phenol, beta hydroxyethyl ethers of glycerol, pentaerythritol, sorbitol, mannitol, etc., condensates of alkylene oxides, such as ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, glycidyl, epichlorohydrin, glycidyl ethers, etc., with polyhydric alcohols, such as the foregoing and with polyhydric thioethers, such as 2,2'-dihydroxydiethyl sulfide, 2,2'-3,3'-tetrahydroxy dipropyl sulfide, etc. The hydroxy aldehydes and ketones may be exemplified by dextrose, fructose, maltose, glyceraldehyde. The mercapto (thiol) alcohols may be exemplified by alpha-monothioglycerol, alpha,alpha-dithioglycerol, etc. The polyhydric alcohol esters may be exemplified by monoglycerides, such as monostearin, monoesters of pentaerythritol and acetic acid, butyric acid, pentanoic acid, and the like. The halogenated polyhydric alcohols may be exemplified by the monochloride of pentaerythritol, monochloride of sorbitol, monochloride of mannitol, monochloride of glycerol, andthe like.

. Other polyether polyepoxides include the polyepoxypolyhydroxy polyethers obtained by reacting, preferably in an alkaline medium, a polyhydric alcohol or polyhydric phenol with a polyepoxide, such as the reaction prodnot of a glycidyl ether of a polyhydric phenol with the same or dilferent polyhydric phenol, the reaction product of glycerol and bis(2,3-epoxypropyl) ether, the reaction product of sorbitol and bis(2,3-epoxy-2-methylpropyl) ether, the reaction product of pentaerythritol and 1,2- epoxy-4,5-epoxypentane, and the reaction product of bisphenol and bis(2,3-epoxy-2-methylpropyl) ether, the reaction product of resorcinol and bis(2,3-epoxypropyl) ether, and the reaction product of catechol and bis(2,3- epoxypropyl) ether.

-A group of polymeric-type polyether polyepoxides comprises the hydroxy-substituted polyepoxide polyethers obtained by reacting, preferably in an alkaline medium, a slight excess, e.g., .5 to 3 mole excess, of a halogen-containing epoxide, such as epichlorohydrin, with any of the aforedescribed polyhydric phenols, such as resorcinol, catechol, 2,2 bis(4' hydroxyphenyDpropane, bis [4 (2 hydroxy naphth 1 yl) 2 2 hydroxy naphth 1 yl] methane, and the like.

Other polymeric polyether polyepoxides include the polymers and copolymers of the allylic ether of epoxy containing alcohols. When this type of monomer is polymerized in the substantial absence of alkaline or acidic catalysts, such as in the presence of heat, oxygen, peroxy compounds, actinic light, and the like, they undergo additional polymerization at the multiple bond leaving the epoxy group unafiected. These allylic ethers may be polymerized with themselves or with other ethylenically unsaturated monomers, such as styrene, vinyl acetate, methacrylonitrile, acrylonitrile, vinyl chloride, vinylidene chloride, methyl acrylate, methyl methacrylate, diallyl phthalate, vinyl allyl phthalate, divinyl adipate, Z-chloroallyl acetate, and vinyl methallyl pimelate. Illustrative examples of these polymers include poly(allyl 2,3-epoxypropyl ether), allyl 2,3-epoxypropyl ether-styrene copolymer, methallyl 3,4-epoxybutyl ether-allyl benzoate copolymer, poly(vinyl 2,3-epoxypropyl)ether and an allyl glycidyl ether-vinyl acetate copolymer.

Coming under special consideration are the polyglycidyl polyethers of polyhydric alcohols obtained by reacting the polyhydric alcohol with epichlorohydrin, preferably in the presence of 0.1% to 5% by weight of an acidacting compound, such as boron trifluon'de, hydrofluoric acid, stannicchloride or stannic acid. This reaction is effected at about 50 C. to C. with the proportions of reactants being such that there is about one mole of epichlorohydrin for every equivalent of hydroxy group in the polyhydric alcohol. The resulting chlorohydrin ether is then dehydrochlorinated by heating at about 50 C. to 125 C. with a small, e.g., 10% stoichiometrical excess of a base, such as sodium aluminate.

The products obtained by the method shown in the preceding paragraph may be described as polyether poly epoxide reaction products which in general contain at least three non-cyclic ether (--O-) linkages, terminal epoxide-containing ether.-

(0.QH2CHCH2) groups and halogen attached to a carbon of an intermediate group.

These halogen-containing polyether polyepoxide reaction products obtainable by partial dehydrohalogenation of polyhalohydrin alcohols may be considered to have the -following general formula GET-J18] in which R is the residue of the polyhydric alcohol which may contain unreacted hydroxyl groups, X indicates one or more of the epoxy ether groups attached to the alcohol residue, y may be one or may vary in difierent reaction products of the reaction mixture from zero to more than one, and Z is one or more, and X+Z, in the case of products derived from polyhydric alcohols containing three or more hydroxyl groups, averages around two or more so that the reaction product contains on the average two or more than two terminal epoxide groups per molecule.

The preparation of one of these preferred polyglycidyl ethers of polyhydric alcohols may be illustrated by the following example showing the preparation of a glycidyl polyether of glycerol.

PREPARATION OF GLYCIDYL POLYETHERS OF POLHYDRIC ALCOHOLS Polyether A About 276 parts (3 moles) of glycerol was mixed with parts of diethyl ether solution containing about 4.5% boron trifluoride. 832 parts of epichlorohydrin was then added dropwise. The temperature of this mixture was between 50 C. and 75 C. for about 3 hours. About 370 parts of the resulting glycerol-epichlorohydrin condensate was dissolved in 900 parts of dioxane containing about 300 parts of sodium aluminate. While agitating, the reaction mixture was heated and refluxed at 93 C. for 9 hours. After cooling to atmospheric temperature, the insoluble material was filtered from the reaction mixture and low boiling substances removed by distillation to a temperature of about 150 C. at 20 mm. pressure. The polyglycidyl ether, in amount of 261 parts, was a pale yellow, viscous liquid. It had an epoxide value of 0.671 equivalent per 100 grams and the molecular weight was 324 as measured ebullioscopically in dioxane solution; The epoxy equivalency of this product was 2.13. For convenience, this product will be referred to hereinafter as Polyether A.

Polyether B 10.5 moles of ethylene oxide was bubbled through 3.5 moles glycerine containing an acid catalyst at 40-50 C. The resulting product had a molecular weight of 224 and a hydroxyl value of 1.417 eq./100 g. 101 parts of this ethylene oxide glycerine condensate was placed in a reaction kettle and heated to 65-70 C. Sufficient BF ethyl ether complex was added to bring the pH to about 1.0 and then 132 parts of epichlorohydrin added dropwise. After all the epi had been added, the reaction was continued for about minutes to assure complete reaction. This product was then dissolved in benzene and 57 parts of sodium hydroxide were added in 7 equal portions at about 87-89 C. over a period of hour and then filtered to remove the salt. The solvent and light ends were then removed by stripping at a low vacuum. The resulting product had a molecular weight of 455, and an epoxy value of .524 eq./100 g. For convenience, this polyether will be referred to herein as Polyether B.

Polyether C One equivalent of 1,2,6-hexanetri0l was placed in a reaction kettle and heated to 6570 C. Sufficient BF ethyl ether complex was added to bring the pH to about 1.0 and then 1 equivalent of epichlorohydrin added dropwise. After all the epi had been added, the reaction was continued for about 15 minutes to assure complete reaction. This product was then dissolved in acetone and sodium orthosilicate was added at about 65 C. over a period of 0.5 hour and then filtered to remove the salt. The solvent and light ends were then removed by a stripping at a low vacuum. The resulting product had a molecular weight of .325 and an epoxy value of .600 eq./100 g. For convenience, this polyether will be referred to herein as Polyether C.

glycidyl polyethers of dihydric phenols obtained by reacting epichlorohydrin with a dihydric phenol in an alkaline medium. The monomeric products of this type may be represented by the general formula 0r ooH20R0oHr-0fi 0m wherein R represents a divalent hydrocarbon radical of the dihydric phenol. The polymeric products will generally not be a single simple molecule but will be a complex mixture of glycidyl polyethers of the general formula C/HZ\O H-GH-O- (-R-O-CHz-CHCH-C Hz- 0 ),.R O-UHz- C/H\O Hg wherein R is a divalent hydrocarbon radical of the dihydric phenol and n is an integer of the series 0, 1, 2, 3, etc. While for any single molecule of the polyether n is an integer, the fact that the obtained polyether is a mixture of compounds causes the determined value of n to be an average which is not necessarily zero or a whole number. The polyethers may, in some cases, contain a very small amount ofmaterial with one or both of the terminal glycidyl radicals in hydrated form.

The aforedescribed preferred glycidyl polyethers of the dihydric phenols may be prepared by reacting the required proportions of the dihydric phenol and the epichlorohydrin in an alkaline medium. The desired alkalinity is obtained by adding basic substances, such as sodium or potassium hydroxide, preferably in stoichiometric excess to the epichlorohydrin. The reaction is preferably accomplished at temperatures within the range of from 50 C. to 150 C. The heating is continued for several hours to effect the reaction and the product is then washed free of salt and base.

The preparation of some of the glycidyl polyethers of the dihydric phenols will be illustrated below.

PREPARATION OF GLYCEDYL POLYETHERS OF DIHYDRIC PHENOLS Polyether D About 2 moles of bis-phenol was dissolved in 10 moles of epichlorohydrin and 1% to 2% water added to the resulting mixture. The mixture was then brought to C. and 4 moles of solid sodium hydroxide added in small portions over a period of about 1 hour. During the addition, the temperature of the mixture was held at about C. to C. After the sodium hydroxide had been added, the Water formed in the reaction and most of the epichlorohydrin was distilled off. The residue that remained was combined with an approximately equal amount of benzene and the mixture filtered to re move the salt. The benzene was then removed to yield a viscous liquid having a viscosity of about poises at 25 C. and a molecular weight of about 350 (measured ebullioscopically in ethylene dichloride). The product had an epoxy value of 0.50 eq./100 g., and an epoxy equivalency of 1.75. For convenience, this product will be referred to hereinafter as Polyether D.

Polyether E A solution consisting of 11.7 parts of water, 1.22 parts of sodium hydroxide, and 13.38 parts of bis-phenol was prepared by heating the mixture of ingredients to 70 C. and then cooling to 46 C. at which temperature 14.06 parts of epichlorohydrin was added While agitating I the mixture.

After 25 minutes had elapsed, there was added during an additional minutes time a solution consisting of 5.62 parts of sodium hydroxide in 11.7 parts of water. This caused the temperature to rise to 63 C. Washing with water at C. to 30 C. temperature was started 30 minutes later and continued for 4 /2 hours. The product was dried by heating to a final temperature of 140 C. in 80 minutes, and cooled rapidly. At room temperature, the product was an extremely viscous semi-solid having a melting point of 27 C. by Durrans Mercury Method and a molecular weight of 483. The product had an epoxy value of 0.40 eq./ 100 g., and an epoxy equivalency of 1.9. For convenience, this product will be referred to as Polyether E.

Particularly preferred members of the above-described group are the glycidyl polyethers of the dihydric phenols, and especially 2,2-bis(4'-hydroxyphenyl)propane, having an epoxy equivalency between 1.1 and 2.0 and a molecular Weight between 300 and 900. Particularly preferred are those having a Durrans Mercury Method softening point below about 60 C.

The glycidyl polyethers of polyhydric phenols obtained by condensing the polyhydric phenols with epichlorohydrin are also referred to as ethoxylene resins. See Chemical Week, vol. 69, page 27, for September 8, 1951.

Of special interest are the polyether polyepoxides containing elements of the group consisting of carbon, hydrogen, and oxygen and chlorine, with the oxygen only contained in the ether and epoxy groups.

The epoxy curing agent employed in the process of the invention may be any alkaline, neutral or acidic material Which acts to effect cure of the polyepoxide to an insoluble product. This includes acid-acting curing agents, such as the organic and inorganic acids and anhydrides as citric acid, phthalic acid, phthalic acid anhydride, tartaric acid, aconitic acid, oxalic acid, succinic acid anhydride, lactic acid, maleic acid, maleic acid anhydride, fumaric acid, glutaconic acid, 1,2,4-butanetricarboxylic acid, isophthalic acid, terephthalic acid, malonic acid, l,l,5-pentanetricarboxylic acid, trimellitic acid, phosphoric acid, boric acid, sulfonic and phosphonic acids, perchloric acid, persulfuric acid, boron-trifluoride complexes, such as the pcresol and urea complex, amino compounds, such as ethylene diamine, diethylene triamine, triethylene tetraamine, dicyandiamide, melamine, pyridine, cyclohexylamine, benzyldimethylamine, benzylamine, diethylaniline, triethanolamine, piperidine, tetramethylpiperazine, N,N dibutyl 1,3 propane diamine,

.N,N diethyl l 3 propane diamine, 2 7 diamino- 2,6-dimethyloctane, dibutylamine, dioctylamine, diallylamine, pyrrolidine, Z-methylpyrrolidine, tetrahydropyridine, Z-methylpiperidine, tetrahydropyridine, 2-methylpiperidine, diaminopyridine, and the like. Salts of inorganic acids, such as zinc fluoborate, magnesium fluoborate, magnesium perchlorate, potassium persulfate, copper fluoborate, copper persulfate, cobaltic fiuoborate, chromic nitrate, magnesium nitrate, calcium phosphite, and the like, as Well as soluble adducts of polyamines and polyamines and polyepoxides, such as disclosed in US. 2,651,589, salts of these adducts as disclosed and claimed in my copending application Serial No. 492,805, filed March 7, 1955.

Preferred curing agents to be employed are the acidic compounds, such as polycarboxylic acids and their anhydrides and salts of metals having an atomic Weight between 24 and 210, and preferably in groups I to IV and VIII of the periodic table of elements and inorganic acids the anion portion of which contains at least two dissimilar elements having an atomic weight above 2, and particularly inorganic acids of the formula wherein X is a non-metal having an atomic weight above 2, Z is an element that gains from 1 to 2 electrons in its outer orbit, such as oxygen and fluorine, w is an integer,

y is an integer greater than 1 and equals the valency of the radical (X) ,,,(Z),,, such as sulfuric acid, fiuoboric acid, fluosilicic acid, persulfun'c acid, phosphoric acid and the like.

Also preferred particularly because of their high activity at the lower temperature, are the soluble adduct of (1) amines having a plurality of amino groups, at least one of which is a primary amino group, and especially amines of the formulae wherein R is a divalent hydrocarbon radical, R is a monovalent hydrocarbon radical, and preferably aliphatic and aromatic hydrocarbon radicals containing no more than 18 carbon atoms, and n is an integer, preferably from 1 to 8, and (2) a polyepoxide, and preferably glycidyl ether of polyhydric alcohol or polyhydric phenol, as well as salts of the above-described adducts and inorganic or organic acids, and especially the aliphatic and aromatic hydrocarbon monocarboxylic acids containing up to 12 carbon atoms, said acids being combined with the adducts in sufficient amount to reduce the pH to at least 9 and preferably neutralize the adduct.

The above-described polyether polyepoxide and epoxy curing agent are applied to the paper pulp or finished paper by means of an aqueous medium. If the paper pulp or paper is already in contact with an aqueous medium as is generally the case in the usual beater method for preparing paper from paper pulp, the polyether polyepoxide and epoxy curing agent may be added as such directly to that aqueous medium. However, if this is not the case, the polyether polyepoxide and epoxy curing agent should be added to an aqueous medium before addition to the paper. Even in the case where the paper pulp or paper is already in contact with an aqueous medium, it is usually highly desirable to first form an aqueous medium containing the polyether polyepoxide and epoxy curing agent before applying them to the paper product. The polyether polyepoxide and epoxy curing agent may be applied separately or together both as such or in the aqueous medium, but in most cases it is preferred to add them at the same time in the same aqueous medium.

If the polyether polyepoxide is water soluble, the aqueous medium may be a straight aqueous solution. However, if the polyether polyepoxide has limited solubility in water, it is desirable to utilize aqueous mediums containing organic solvents or emulsifying agents. Solvents suitable for this purpose include, among others, lower alkanols, as ethyl alcohol, propyl alcohol, isobutyl alcohol, alkyl ketones, such as acetone, methyl ethyl ketone, esters, ethers, dioxane, diacetone, and the like, and mixtures thereof. Emulsifying agents employed are preferably the acid and alkali stable non-ionic emulsifying agent. The expression acid and alkali stable means that the aqueous emulsions prepared from such agents must be stable, i.e., must not coagulate or settle out, when contacted with acids, such as, for example, 5% hydrogen chloride, or bases, such as, for example, 5% sodium hydroxide. The expression non-ionic" refers to those compounds which are not salts and subject to ionization when dissolved in water. Examples of these agents include, among others, partial esters of polyhydric alcohols and saturated or unsaturated fatty acids and preferably fatty acids containing at least 6 and more preferably from 12 to 18 carbon atoms. These esters preferably have less than a majority of the hydroxyl groups of the polyhydric alcohol csteritied or acylated. These include particularly the fatty acid esters of inner ethers of hexitol, especially those monoesters of saturated or unsaturated fatty acids of 12 to 18 carbon atoms and hexitans and hexitides such as sorbitan or mannitan monolaurate, monopalmitate, monostearate, mono-oleates, or the monoesters of coconut oil fatty acids and like products described in US. 2,322,820. Other examples of partial esters of this type include the pentaerythritol monoand di-palmitate, pentaerythritol monoand di-stearate, pentaerythritol monoand di-oleate, 1,2,6-hexanetriol monoand di-caprate, 1,2,6-hexanetriol monoand di-oleate, trimethylolpropane distearate, trimethylolpropane dilaurate, polyglycerol dilaurate, inositol monolaurate, glucose monostearate, sucrose mono-oleate, polyglycol mono-oleate, polyglycol monostearate, and the like.

Examples of other suitable non-ionic emulsifying agents include the hydroxypolyoxyalkylene ethers of the above described partial esters. Preferred members of this group include the polyalkylene oxide with thefatty acid esters of the inner ethers of hexitol in the manner described in U.S. 2,380,166. Specific emulsifiers of this class include, among others, the polyethylene glycol ethers of sorbitan or mannitan monolaurate, monopalmitate, mono-oleate or monostearate. Other examples include the polyethylene glycol ethers or pentaerythritol monoand dipalmitate, pentaerythritol monoand di-stearate, pentaerythritol monoand di-oleate, trimethylpropane distearate, polyglycerol dilaurate, inositol monolaurate, glucose monostearate and the like.

Examples of other suitable non-ionic emulsifying agents include the diand mono-ethers of polyhydric compound and particularly the polyalkylene glycols. Especially preferred are the aryl and alkaryl polyethylene glycol ethers such as phenyl polyethylene glycol monoether, xylyl polyethylene glycol monoether, isopropylphenyl polyethylene glycol monoether and the like.

The amount of the emulsifying agent employed in preparing the emulsions will vary over a considerable range. In general, the amount of the agent will vary from about 1% to 100% by weight of the polyether polyepoxide, and more preferably from 3% to 40% by weight of the polyether polyepoxide. The above-described partial fatty acid esters of polyhydric alcohols. and their partial ethers are preferably employed in amounts varying from about 3% to 30% by weight of the polyepoxide.

Water-dispersible binding colloids are also preferably utilized in the emulsions. These preferably include the polyvinyl alcohols, homopolymers and copolymers of unsaturated acids, such as methacrylic acid, maleic acid and fumaric acid with other unsaturated monomers, such as vinyl ethers styrene, alpha-methylstyrene, acrylonitrile, vinyl acetate, vinyl chloride, methyl ethacrylate, vinylidene chloride, and the like, polymers of vinyl esters which have been partially deacylated so as to render them waterdispersible, such as partially deacylated polyvinyl acetate, polyvinyl butyrate, polyvinylbenzene, and the like, and salts of such polymers and copolymers. Examples of other suitable binding colloids include methylcellulose carboxymethylcellulose, starch, gelatine, starch degradation products such as dextrine, and the like, and mixtures thereof.

Preferred water-dispersible binding colloids to be used include the polyvinyl alcohols such as those obtained by partial hydrolysis of polyvinyl acetate, carboxymethyl cellulose, methyl cellulose and copolymers of maleic acid.

Particularly preferred are the polyvinyl alcohols obtained by partial hydrolysis of polyvinyl acetate. The available products of this type generally have low, medium or high viscosities and have a degree of hydrolysis varying from about 45% to 99%. Of special interest are the polyvinyl alcohols having high viscosity and a degree of hydrolysis of at least 75%.

The water-dispersible binding colloid should be employed in the emulsion in amounts varying from about .1% to 15% by weight of the polyepoxides. Preferably the binding colloid is utilized in amounts varying from 3 to by weight of the polyepoxide.

The aqueous emulsion of the polyether polyepoxide using the above-noted emulsifying agents and water-dispersible binding colloid is preferably prepared by merely mixing the components together as in Example I, or as in the case of the more insoluble polyether polyepoxides (as in Example IV). by mixing the polyepoxide with the emulsifying agent, adding the water-dispersible binding colloid and then adding warm or hot water with slow stirring until the emulsioninverts. Following the inversion, warm to hot water can be added as rapidly as desired to bring the emulsion up to the desired solution. In some cases, the polyepoxide will be in solid form and it may be necessary to melt the material at temperature below about C. before it can be mixed with the emulsifying agent.

Other materials may also be added to the aqueous medium to provide paper for special applications. Thus, if one desires paper having improved water repellency they may add organic compounds having a continuous chain of at least 12 aliphatic carbon atoms and at least one functional group reactive with epoxy groups, such as, for example, havinga chain of from 12 to 30 carbon atoms and functional groups, such as an epoxy group, anhydride group, phenolic hydroxyl group, amine or substituted amine group, amide group, carboxyl group, sulfonic acid, group, mercapto, group, aldehyde group or acetylenic group, as octadecyl succinic anhydride, eicosylsuccinic acid, octadecylamine, N-octadecyl propylamine, glycidyl dodecyl ether, glycidyl octadecyl ether, pentadecylphenol, pentadecanethiol, eicosanesulfonic acid, and the like, and mixtures thereof, preferably in amounts varying from one-third to 1.5 times that of the polyepoxide described above. 7

The amount of the polyether polyepoxide to be present in the aqueous medium will depend upon the amount of the polyepoxide to be applied to the paper. For most applications, it is preferable to apply from .1% to 30% by weight (based on weight of paper) of the polyepoxide, and more preferably from 1% to 20% by weight. If the polyether polyepoxide is added during the beater stage, the material shouldgbe added in a slight excess of the desired amount. If'the polyether polyepoxide is to be applied by impregnating an already formed paper, the amount in the impregnating solution will depend upon the pick-up allowed. If a. 100% pick-up is allowed and the solution is applied but once, the aqueous medium should contain the polyether polyepoxide in amounts corresponding to that desired on the paper. On the other hand, if say only a 50% pick-up is allowed and the solution is applied but once, the polyether polyepoxide should be added to the aqueous medium inv amounts which are about twice that required on the finished paper.

The amount of the curing agent employed will vary depending upon the type of agent selected. In general, the amountof the curing agent will vary from about 0.5% to 40% by weight of the polyether polyepoxide. The acids are preferably employed in amounts varying from about 0.5% to 20% by weight, the metal salts, soluble adducts and salts of the adductsare preferably employed in amounts varying from 1% to 30% by weight, and the anhydrides are preferably employed in stoichiometric amounts, i.e., about one anhydride group for every epoxy group.

As indicated above, the polyether polyepoxide and epoxy curing agent may be appliedto the paper pulp or paper at any stage during the preparation of the paper up to and including the finishedpaper. Preferably the materials are added during the beater stage when the suspension of the paper pulpis being rapidly agitated or are added-directly to the finished sized or unsized paper. If the materials are added during the beater stage, the beater operations may be any of those now used for this purpose. Onemerely needs to pour or otherwise add the polyether polyepoxide and epoxy. curing agent, preferably in the form of the aqueous medium, directly to the aqueous suspension of pulp either all at once or intermittently over a short period of time.

If the polyether polyepoxide and epoxy curing agent are to be applied to the finished paper, they may be added by spraying, by rollers, by dipping or by running the paper through a conventional-type padding apparatus.

After the polyether polyepoxide and epoxy curing agent have been applied to the paper as indicated above, the treated product is subsequently dried to remove some or all of the dispersing liquid.

If the material is applied during the preparation of the paper, the pulp is formed into paper sheets and these sheets then dried to remove the dispersing liquid. The drying may be accomplished by exposing the wet paper to hot gas at temperatures ranging from about 80 C. to 100 C. or more preferably as in commercial operations by passing the paper over hot rolls. The period of drying will depend largely on the amount of pick-up and the concentration of the polyether polyepoxide. In most instances, drying periods of from 1 to 30 minutes should be sufiicient.

Cure of the polyester polyepoxide is then effected. If the curing agent employed is one that is active at the lower temperature, the curing may be eifected by merely allowing the paper to stand at or near room temperature after the drying period. With the less active curing agents, the cure is accomplished by heating, preferably at temperature between 100 C. to 200 C. for a few minutes.

Any type of paper may be treated according to the process of the invention. Examples of such paper include, for example, those prepared from wood, cotton, linen, hemp, jute, mulberry, straw, bamboo, cane and agone fibers or mixtures thereof, by any of the known processes such as the sulfate process, soda process and sulfite process. The paper may be colored or white and may be further treated for special applications.

The paper treated according to the process of the invention may be used for a variety of applications such as facial tissue, hand towels, maps, filing cards, construction paper, wrapping paper, containers and the like. Because of its resistance to hydrolyses and relative non-toxic nature, the paper is particularly suited for use in preparing wrapper or containers for food.

To illustrate the. manner in which the invention may be carried out, the following examples are given. It is to be understood, however, that the examples are for the purpose of illustration and the invention is not to be regarded as limited to any of the specific materials or conditions recited therein.

EXAMPLE I This example illustrates the improvement in properties obtained by treating paper with an aqueous medium of Polyether A.

An aqueous solution was prepared as follows: 150 parts of Polyether A, 7.5 parts of a polyethylene glycol monostearate and 150 parts of water were mixed together. To this mixture was added 75 parts 5% solution of partially hydolyzed polyvinyl acetate, 400 parts of water and 100 parts of an aqueous solution containing 10.8 parts of zinc fluoborate water was then added to-bn'ng the total to 1000 so as to give a 15% resin solution. 5% and 2.5% solutions were prepared by adding the necessary amount of water to portion of the abovedescribed resin solution.

Pieces of unbleached kraft paper were then treated with the 10%, 5% and 2.5% solutions by means of a Butterworth 3-roll laboratory padder. The sheets after impregnationshowed a 85% wet pick-up. The treated sheets were then dried and heated for 5 minutes at 160 C. The resulting sheets had the same feel and appearance as before the treatment and displayed excellent resiliency, good fold endurance, good absorbency and high wet tensile strengths and burst strengths. The

'Mullen burst strengths (TAPPI T 403 m-53) of each of the sheets are shown below in comparison to the un treated sheets:

1 Samples soaked 4 hrs.

20%, 15%, 10%, 5% and 2.5% solutions were prepared as noted above and these were applied to the unbleached kraft paper in the above-described manner. The sheets after impregnation showed an wet pickup. The resulting sheets had the same feel and appearance as before the treatment and displayed excellent resiliency, good fold endurance, good absorbency and high wet tensile strengths and burst strengths. The tensile strengths (T-404 m-50) of each of the sheets are shown below in comparison to the untreated sheets:

Tensile Strengths, lbs/inch Amount of resin in Treating Solution Dry Wet 1 Percent Retention 1 Samples soaked 4 hours.

EXAMPLE II This example illustrates the improvement in properties obtained by treating paper with Polyether D.

An aqueous emulsion was prepared as follows: parts of Polyether D was combined with 10 parts of a polyethylene glycol ether or sorbitan monopalmitate at 100 C. 100 parts of a 5% solution of polyvinyl alcohol and 25 parts of an acetate acid salt of an adduct of triethylene diamine-polyether D adduct prepared as shown in Example I of my copending application Serial No. 492,801, were then added and additional Water added to bring the solution up to 1000 parts. 5% and 2.5% solutions were prepared by adding the necessary amount of water to portions by the above solution.

Pieces of untreated kraft paper were then treated with each of the above solutions by means of a Butterworth 3-roll laboratory padder. The sheets after impregnation showed an 85 Wet pick-up. The impregnated sheets were then dried and heated for 5 minutes at C. The resulting sheets had the same feel and appearance as before the treatment and displayed excellent resilience, good fold endurance, good absorbency and surprisingly high wet tensile strengths.

Paper having related properties are obtained by replacing Polyether D in the above process with equivalent amounts of each of the following: Polyether E and a glycidyl polyether of 2,2-bis(4-hydroxyphenyl)butane.

EXAMPLE III This example illustrates the improvement in properties obtained by adding an aqueous emulsion of Polyether A directly to the beater.

Unbleached kraft paper pulp was beaten in a Valley" beater in the usual manner and made into a 0.6% water suspension. A portion of the aqueous emulsion of Polyether A prepared as in Example I is added to the paper pulp suspension so as to give a solution having 3% resin based on the weight of the paper pulp. This suspension was then made into a paper sheet and the sheet dried 13 for a few minutes at 60 C. The dried sheet is then heated for minutes at 160 C. The resulting sheet appeared as normal paper but displayed excellent resiliency, good fold endurance, good absorbency and had surprisingly high wet strength.

Paper having related properties is obtained by replacing Polyether A solution in the above process with equivalent amounts of each of the following: Polyether B, Polyether C and Polyether D.

EXAMPLE IV This example illustrates the improvement in properties obtained by treating paper with Polyether D and an anhydride as curing agent.

An aqueous medium was prepared as follows: 8.0 parts of Polyether D and 10.8 parts of chlorendic anhydride were melted together and .8 part of a polyethylene glycol ether of sorbitan monopalmitate added. 8.0 part of 5% aqueous polyvinyl alcohol (77% partially hydrolyzed polyvinyl acetate) was added slowly with stirring. Water was then added to produce a 20% resin solution.

Bleached southern kraft paper was then treated with this solution by means of a Butterworth 3-roll laboratory padder. The sheets after impregnation showed a 80% wet pick-up. The treated sheets were then dried and heated for 5 minutes at 160 C. The resulting sheets had the same feel and appearance as before the treat ment and displayed excellent resiliency and flexibility and good wet strength.

Paper having related properties is obtained by replacing the chlorendic anhydride with chloromaleic anhydride and the Polyether D with Polyether E.

EXAMPLE V This example illustrates the improvement in properties obtained by treating paper with polyallyl glycidyl ether and magnesium perchlorate as the catalyst.

An aqueous emulsion was prepared as follows: 20 parts of polyallyl glycidyl ether having a molecular weight of 481 and epoxy value of 0.50 eq./ 100 grams was mixed with 2 parts of a polyethylene glycol monostearate. To this mixture was added 20 parts of warm 5% aqueous polyvinyl alcohol (80% partially hydrolyzed polyvinyl butyrate) solution with stirring. Warm water was then added slowly until the emulsion inverted and then water added to bring the total solution up to 20% resin solution. About 1.0 part of magnesium perchlorate was added to this emulsion and the emulsion padded on untreated kraft paper by means of the Butterworth 3-roll laboratory padder. The treated sheet was then dried and heated at 160 C. for 5 minutes. The resulting treated sheet has good feel and appearance and displayed excellent resiliency and good wet strength.

I claim as my invention:

1. A process for producing wet strength paper having improved properties comprising applying at some time during the production of paper from paper pulp up to and including the finished paper, by means of an aqueous medium (1) from .1% to 30% by weight of the paper of a polyether polyepoxide and (2) an epoxy curing agent to the paper product present at that stage, and heating at a temperature between 100 C. and 200 C. to efiect cure of the polyepoxide.

2. A process for producing wet strength paper having improved properties which comprises adding an aqueous medium containing a polyether polyepoxide and an epoxy curing agent to an aqueous suspension of paper pulp at the beater stage, forming paper from the resulting 14 product, drying the paper and then heating at a temperature between C. and 200 C. to effect cure of the polyepoxide, the amount of the polyether polyepoxide employed being suflicient to apply to the paper from 1% to 20% by weight of the said paper.

3., A process as in claim 2 wherein the polyether polyepoxide is a glycidyl polyether of an aliphatic alcohol.

4. A process as in claim 2 wherein the polyether polyepoxide is a halogen-containing polyether polyepoxide composition which composition is a mixture of ethers of polyhydric alcohols, the polyhydric alcohols having from 2 to 5 hydroxyl groups with at least two of the hydroxyl groups replaced in part by the group 0 -OCH:-O CHa and in part by the group and any hydroxyl groups which are not so replaced being unchanged hydroxyl groups.

5. A process as in claim 2 therein the polyether polyepoxide is a glycidyl polyether of a polyhydric phenol.

6. A process as in claim 2 wherein the epoxy curing agent is an acidicv compound.

7. A process for preparing paper having improved wet strength which comprises impregnating already formed paper with an aqueous medium containing a polyether polyepoxide and an epoxy curing agent so as to apply to the paper from 1% to 20% by weight of the paper of the said polyether polyepoxide and heating at a temperature between 100 C. and 200 C. to efiect cure.

8. A process as in claim 7 wherein the polyether polyepoxide is a glycidyl polyether of an aliphatic polyhydric alcohol.

9. A process as in claim 7 wherein the polyether polyepoxide is a glycidyl polyether of a polyhydric phenol.

10. A process as in claim 7 wherein the aqueous medium is an aqueous emulsion containing a glycidyl polyether of a polyhydric alcohol, a non-ionic emulsifying agent and a stabilizer comprising a polyhydric alcohol.

11. A process as in claim 7 wherein the curing agent is a salt of (1) a metal having an atomic weight between 24 and 210, and (2) an inorganic acid the anion portion of which contains at least two dissimilar elements having an atomic weight above 2.

12. A process as in claim 7 wherein the epoxy curing agent is a salt of an organic acid and a soluble adduct of a polyamine and a polyepoxide.

13. A process as in claim 7 wherein the epoxy curing agent is zinc fluoborate.

14. A product prepared by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 

7. A PROCESS FOR PREPARING PAPER HAVING IMPROVED WET STRENGTH WHICH COMPRISES IMPREGNATING ALREADY FORMED PAPER WITH AN AQUEOUS MEDIUM CONTAINING A POLYETHER POLYEPOXIDE AND AN EPOXY CURING AGENT SO AS TO APPLY TO THE PAPER FROM 1% TO 20% BY WEIGHT OF THE PAPER OF THE SAID POLYETHER POLYEPOXIDE AND HEATING AT A TEMPERATURE BETWEEN 100*C. AND 200*C. TO EFFECT CURE. 